This invention relates to a method and apparatus for use in an oil well or other drilling operation in which drilling fluids are used and recycled. More particularly, the invention relates to a novel method and apparatus for reclaiming valuable drilling fluids which are discarded with the solids in the drilling rig separation process.
In the drilling of oil wells and other drilling operations, drilling fluids, commonly called DRILLING MUD OR MUD, are circulated down the borehole to lubricate the process and carry away the broken bits of rocks and debris created in the drilling. Another important function of the mud is to provide a static hydraulic head in the borehole sufficient to equal the pressure of any formation encountered thus preventing leakage of production fluids up the annulus around the drill pipe. For the latter reason different weights of MUD are used. WEIGHTED MUD is a drilling fluid to which heavy (over 2.6 Specific Gravity) solids have been added to increase the weight of the SLURRIED MUD. Conversely UNWEIGHTED MUD is a SLURRIED MUD that contain no commercial solids significantly heavier than 2.6 specific gravity.
New particles of drilled solids are brought to the top of the borehole with each circulation of the MUD. These particles vary in size from colloidal (average diameter less than 0.5 micron) to the largest that can be lifted and will pass through the annulus between the drill pipe and the borehole. If the particles are not removed, they will be pumped back down the hole either to increase the thickness of the solids deposited on the borehole wall or to return to the surface. As they are circulated they are ground into smaller particles by the drilling process and become increasingly difficult to remove. When, and if the smaller particles are removed, they will take more drilling fluid with them. If simply discarded, the accompanying drilling fluids are lost. Further, disposal creates a solid pollution problem which in some locations is illegal.
The refuse from the drilling operation is generally disposed of in a "reserve" pit. The reserve pit can thus become a large area which may spill over onto adjacent farmland and crops causing environmental and legal problems. When drilling in waters such as offshore the pollution caused by the discharge of the refuse is not ony undesirable, but also sometimes illegal.
Further, the refuse from the drilling operations still contains considerable amounts of valuable drilling fluids. When the recovery of the drilling fluid is combined with a reduction in cost due to elimination of reserve pits or tanks, overall economics of the drilling operation are improved.